Enable cups for all packages?

Hi,
it is possible to enable cups support for single package like using
PKG_OPTIONS.ghostscript = cups
But how do I enable it for all packages, without finding out all current
packages and keeping the PKG_OPTIONS.* list up to date with every new
cups support for a package?
I don't want to get into trouble like now with firefox3, where I was told
that it depends on cups support in gtk2.
Another option would be to enable it by default, but I don't think
that everyone wants that here.
Bernd